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Greyscale-density calibration of an industrial CT scanner for wood microdensitometry

Kadas, Marios (2016-03)

Thesis (MScFor)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: The microdensitometry of wood, that is the quantification of density in the micrometre scale, is
important for different scientific disciplines such as wood science, dendrochronology,
dendroecology, dendroclimatology, and biomass determination and in the industrial
applications of engineered wood. With the advent of industrial computed tomography
scanners, powerful equipment for density measurement is available. However, the
methodological framework for wood density determination with those machines is not fully
established, because possible error sources have not so far been analysed and described
sufficiently. Thus, the objective of this study was the development of a methodology, in order
to quantify wood density with an industrial computed tomography scanner.
In this study, industrial cone-beam computed tomography was used for the microdensitometry
of wood. Fifty stacks of stem discs from an equal number of Pinus radiata trees were used as
the sample dataset. Firstly, the fifty stacks were scanned along with selected reference
materials, which were measured for density in a conventional way. Then, fifty linear
regressions were performed between the conventionally-determined density and the grey
value of the reference materials. A strong correlation (mean R2=0.998) between
conventionally-determined density and grey value was observed. The regressions also
provided calibration equations, which could translate a given grey value to a certain density.
For validation purposes, the fifty calibration equations were tested on extra reference
materials. The density from the computed tomography scanner had a mean absolute error of
0.008 g/cm3 (σ=0.004) and a mean percent error of 1.4% (σ=0.7). Additionally, one of the
calibration equations was applied to the creation of tree ring density profiles. An important
result of the study was that it was not possible to deduce a sole calibration equation, as
typically done with densitometers and medical computed tomography scanners. Thus, the
calibration of each scan was inevitable, due to the various degrees of freedom of the
industrial computed tomography scanner.